We describe the effect of gelatinous plankton -Aurelia aurita and invaders Mnemiopsis leidyi and Beroe ovata- on fish (eggs, larvae, feeding, and stocks) in the Black Sea and Sea of Azov, based on field data and the relevant literature. Representatives of three ecological groups of fish were chosen as examples: planktivorous anchovy typical of warrn-water conditions, planktivorous sprat of temperate waters, and benthivorous and piscivorous Black Sea whiting of temperate waters. Changes were noticeable in all three groups, particularly after the invasion of the ctenophore Mnemiopsis leidyi. When the density of the latter decreased, some improvements in fish stocks were recorded, which increased after the invasion of Beroe ovata, predator of Mnemiopsis.